Mobility in Robotic Space

The state of the art in robotic space mobility (e.g. not including conventional rocket propulsion) includes the Mars Exploration Rovers and the upcoming Mars Science Laboratory, and for human surface mobility the Apollo lunar roving vehicle used on the final three Apollo missions. Recently, systems have been developed and tested on Earth for mobility on planetary surfaces including the Space Exploration Vehicle and the ATHLETE wheel-on-leg cargo transporter. Both feature active suspension. A series of grand challenges have extended the reach of robotic off-road mobility to high speeds and progressively more extreme terrain.

For microgravity mobility, the Manned Maneuvering Unit (MMU), tested in 1984 and, more recently, the SAFER jet pack provide individual astronauts with the ability to move and maneuver in free space, or in the neighborhood of a Near-Earth Asteroid. The AERCam system flew on STS-87 in 1997 as the first of future small free-flying inspection satellites. We can expect in the next few decades that robotic vehicles designed for planetary surfaces will approach or even exceed the performance of the best piloted human vehicles on Earth in traversing extreme terrain and reaching sites of interest despite severe terrain challenges.

Human drivers have a remarkable ability to perceive terrain hazards at long range and to pilot surface vehicles along dynamic trajectories that seem nearly optimal. Despite the limitations of human sensing and cognition, it is generally observed that experienced drivers can pilot their vehicles at speeds near the limits set by physical law (e.g. frictional coefficients, tipover and other vehicle-terrain kinematic and dynamic failures). This fact is remarkable given the huge computational throughput requirements needed to quickly assess subtle terrain geometric and non-geometric properties (e.g. visually estimating the properties of soft soil) at long range fast enough to maintain speeds near the vehicle limits. This ability is lacking in today’s best obstacle detection and hazard avoidance systems.